Hydraulic systems on modern construction and other types of mobile equipment have a widely changing flow and load requirements. In some of these systems, a fairly recent concept called "pressure compensation" has been adopted. The basic component of such a system is a pressure compensated flow regulator. This device allows a precise controlled flow to a motor or actuator regardless of the load. The benefits of this controlled flow become most apparent where conditions cause a wide variance in pressures, either upstream or downstream, of the control. The control is accomplished by means of a pressure compensator plunger positioned by servo chambers at opposite ends of the plunger which sense a pressure drop across an orifice in series with the plunger in the controlled circuit and maintain a constant flow across that orifice. Any time the flow across that orifice exceeds the desired level, the pressure drop increases and is sensed on one end of the plunger causing it to automatically throttle-down its flow so as to supply only the fluid necessary to maintain the required pressure drop.
More recently this feature has been incorporated into adjustable flow regulators and also directional control valves in several manners to achieve many different benefits. Examples of these type of systems are shown in U.S. Pat. No. 3,979,908, No. 3,815,477, No. 3,771,558, No. 3,744,517 and No. 3,693,506.